Connecting cord



May 2, 1961 D. J. ANDREW ET AL 2,982,210

CONNECTING coma Filed June 25, 1 958 INVENTORS DAVID J. ANDREW ROBERT W. FELCH GEORGE A. NODDIN ATTORNEY United States Patent CONNECTING CORD David J. Andrew, Simsbury, Conn., and Robert W. Felch, Wenonah, and George A. Noddin, Sewell, N.J., assignors to The Ensign-Bickford Company, Simsbury, Conn., a corporation of Connecticut Filed June 25, 1958, Ser. No. 744,586

1 Claim. (Cl. 102-27) The present invention relates to a novel explosive connecting cord. More particularly, the present invention relates to an explosive connective cord characterized by uniform high velocity, low-brisance, and production of little or no noise. This application is a continuationin-part of our application Serial No. 597,145 filed July 11, 1956, now abandoned.

For many years, detonating fuse was prepared by filling a lead tube with a detonating explosive, particularly trinitrotoluene, and drawing the tubing down to a diameter of about 0.200 inch, thus producing a fuse having an explosive content of about 91 grains per linear foot. Because of the weight and cost of the lead tubing, a textilecovered detonating fuse was developed. In view of the low sensitivity of unconfined trinitrotoluene, in the textilecovered detonating fuse an explosive core of pentaerythritol tetranitrate (PETN) or cyclotrimethylenetrinitramine (RDX) was used. This detonating fuse, which has essentially completely replaced lead-covered detonating fuse in the United States, is prepared in loads ranging from 30 to 400 grains of explosive per linear foot of fuse.

Detonating fuse is widely used in blasting operations to initiate the explosive charges. The detonating fuse possesses the characteristics of uniform high velocity (approximately 6300 meters per second for 40 grains per foot PETN fuse), freedom from likelihood of accidental initiation from impact, stray electricity, atmospheric electricity, (or thunder storm), excellent resistance to water and other fluids, and the ruggedness and strength needed for use under adverse field conditions. The foregoing characteristics, which are highly advantageous, are accompanied by high brisance (shattering power) and considerable noise. Although detonating fuse is relatively safe to handle and use because of its insensitivity with respect to sparks, friction, and ordinary shocks, its high brisance is such that an accidental initiation of a coiled length of fuse may give rise, through the lateral transmission of the detonation stimulus between adjacent portions of the length, to the simultaneous detonation of the entire mass of explosive within the length. Although such occurrences are far from common, they do constitute a safety hazard, if and when they do occur, because the total mass of explosive may be quite high. Moreover and more important. in many operations where the initiation lines must pass objects which will not withstand a shattering explosive force or where noise must be held to a minimum, detonating fuse cannot be used, or elaborate, expensive, and time-consuming shielding, such as, for example, burying the entire length of fuse, must be employed.

Other known methods of conducting an initiation to the explosive charge from a remote area possess so many disadvantages that the shielding techniques are widely used. Electrical initiation means have the disadvantage of requiring long lengths of wire which are subject to severance. loss of insulation, or short-circuiting so as to produce firing failures. The electrical initiation means ice also require considerable care in making proper circuit connections when a large number of charges are to be initiated at one time or when short-delay interval firing is to be used. Even more serious, however, is the susceptibility of electrical initiation means to premature ignition because of extraneous electricity. The sources of extraneous electricity include lightning, static, stray currents, radio transmitters, galvanic action, and transmission lines. Safety fuse is not suitable because of the low burning rate to seconds per year) and the lack of uniformity of burning rate. The burning rate of safety fuse is affected by altitude, weather, tamping, confinement, and handling, so that the rate may vary as much as l0% in either direction from the standard burning speeds.

In addition to applications in which shielding of the fuse, while expensive and time consuming, is effective, there are other applications in which adequate shielding is not feasible. One such application is in blasting wherein initiation of the bottom charge in a borehole prior to initiation of the remaining charges is desired. This blasting procedure, known as bottomhole priming, is used because of evidence that greater blasting efilciency may result from initiation of the explosive in the part of the borehole having the greatest burden. The brisance of detonating fuse is such that the upper charges of explosive will be initiated by the passage of the detonating impulse if dynamite is used as the blasting explosive, whereas, if the very insensitive ammonium nitrate explosives are used, the containers will be destroyed and the contents scattered thus subjecting the soluble salts to the moisture within the borehole, and reducing the continuity of the charge. Therefore, only electrical initiation means, with all attendant disadvantages, have been used in this blasting method.

An object of the present invention is to provide an explosive connecting cord which retains the advantages of detonating fuse but which is considerably less brisant and produces less noise. A further object of the present invention is to provide a connecting cord having all the safety features of detonating fuse with the additional advantage of being incapable of lateral transmission of the detonation stimulus. Additional objects will become apparent as this invention is more fully described.

We have found that an explosive connecting cord which will propagate initiation at a uniform high velocity and which has little brisance and produces very little noise comprises a core of a crystalline cap-sensitive high explosive of such diameter as to contain from 0.1 to 2 grains per foot of explosive encased within a metal sheath, the high explosive being PETN, RDX, HMX (cyclotetramethylenetranitramine), lead azide or styphnate, nitromannite, picryl sulfone, or bis(trinitroethyl)urea.

The metal sheath may be covered with a fabric countering or with a coating of a flexible plastic material such as polyethylene, polyvinyl chloride, etc. Such countering or coating aids in strengthening the cord, improving its appearance, and facilitates its use with conventional blasting supplies such as delay blasting caps, connecting devices, etc.

In order to more fully illustrate this invention, reference is now made to the accompanying drawings in which Figure l is a sectional view of a finished connecting cord of this invention and Figure 2 is an end view of the same cord.

Referring now to the drawings in greater detail, in Figures 1 and 2, 1 represents an explosive core, 2 represents a metal sheath surrounding core 1, and 3 represents a non-metallic countering around sheath 2.

To further describe this invention, reference is now made to specific examples of connecting cord; the examples, of course, are illustrative only, the invention not being limited thereby.

Example I A thirty-foot length of lead tubing having an outside diameter of 0.406 inch and an inside diameter of 0.095 inch was loaded with 1200 grains of finely divided PETN. By passage through a series of dies, the loaded tube was drawn to an outside diameter of 0.092 inch. The explosive core had a diameter of about 0.020 inch and amounted to 1.9 grains of PETN per linear foot of cord.

A waxed fabric countering was applied to a portion of the drawn tubing to form a connecting cord having an outside diameter of 0.195 inch.

The cord thus produced could readily be initiated by a conventional blasting cap butted against or near a cut end of the cord, and the detonation was propagated through the connecting cord at a uniform velocity of 5,800 meters per second. An ordinary blasting cap was readily initiated by an end of the cord inserted into the cap shell in the usual manner. Thus, the connecting cord functioned satisfactorily as a carrier of an initiating impulse at a uniform high velocity.

When the center cord of three adjacent cords was initiated, neither of the side two cords was damaged or initiated by the detonation of the center cord. When a length of the cord was placed on aluminum sheet thicker than 0.051 inch, no indentation occurred and only surface marking was observable. On aluminum sheet of thickness between 0.016 and 0.05l inch, only denting occurred, no rupture being observed. When the cord was placed on the aluminum sheet only, 0.072 inch in thickness, and confined by a covering of putty, only surface marking could be observed, and no denting occurred.

The cord could be tied in knots without interfering in the propagation of the detonation pulse and without a cut-off at the knot. This continuity of propagation is surprising in view of the known failure of the cordeautype of fuse to propagate through knots.

When lengths of the described cord, both with and without the fabric countering, were in either loose or compressed black powder, the black power remained unignited by detonation of the cord. When a length of the cord having a fabric countering was taped lengthwise to a standard dynamite cartridge (containing 40% nitroglycerin), the cartridge was not initiated. Similarly, when a length of uncountered cord within a rubber tub- 1ng was taped to the side of a similar dynamite cartridge, no initiation occurred. No puncture of a metal container for ammonium nitrate explosive compositions resulted from detonation of a length of the cord adjacent to the container.

Example 2 A length of explosive connecting cord was prepared by placing a ribbon of aluminum foil over a block having a -inch square groove and carefully pressing the central portion of the foil into the groove to line the groove. Dry powdered nitromannite was tamped into the groove to produce a square column having approximately 1.0 grain of the explosive per foot of length, and the remaining foil was wrapped around the column of the explosive. The column propagated detonation at a uniform velocity of 3100 meters per second. A leadsheathed core of nitromannite prepared in accordance with the method of Example 1 and containing 1.9 grain per foot of the explosive detonated at a velocity of 5600 meters per second.

Example 3 An extruded column of lead azide granules cemented with nitrocellulose (96 parts by weight of the azide per 4 parts by weight of nitrocellulose) containing approximately 0.5 grain of lead azide per foot was wrapped in aluminum foil. Propagation of detonation at a uniform velocity of L800 meters per second was attained. A leadsheathed cord containing 1.0 grain per foot of lead azide propagated the detonation at a uniform velocity of 2500 meters per second.

Example 4 A connecting cord containing 2.0 grain per foot of RDX encased in a lead tube having an outside diameter of about 0.092 inch and an inside diameter of about 0.020 inch propagated detonation at a uniform velocity of 4200 meters per second.

Example 5 A length of connecting cord consisting of PETN in a lead sheath was prepared in which the outside diameter of the sheath was 0.l37 inch, the core diameter was 0.004 inch, and the PETN amounted to approximately 0.1 grain per foot of length. This cord propagated detonation at a velocity of 3,100 meters per second. A similar cord in which 0.2 grain per foot of PETN was present was also prepared and this cord propagated detonation at a velocity of 4,200 meters per second. In neither cord was the lead sheath ruptured by the detonation of the explosive core.

Example 6 Connecting cords were prepared by the procedure described in Example 1, except that HMX (cyclotetramethylenetetranitramine) was substituted for PETN. The cords which contained 1.9 and 0.9 grain of HMX per foot propagated detonation at a uniform velocity, the detonation velocity of the cord of the latter loading being 5500 meters per second.

Example 7 A series of lead-sheathed cords containing various high explosives in various loadings were prepared by the method of Example 1. The cords, their explosive component and loadings, and their velocity of detonation are summarized in the following table.

Cord Explosive Loading Velocity (gr./t't.) (m.lsec.)

Lend styphnate.-. 1. 2 2. 400 Plcryl snltono 1. 2 4. 760 0. 65 3. 960 0.18 3, 300 BTNEU 1.9 5.750 1. 2 5,100 0.68 4, 700 0.35 3. 800 0.10 3.600

I BTNEU: bis(trinitroethyl)urea.

In contrast, lead-sheath cords containing trinitrotoluene or tetryl in loadings of 2 grains per foot will not propagate the detonation, trinitrotoluene cords failing at a loading of 4.5 grains per foot.

As the foregoing examples illustrate, we have found that an explosive core of 0.1 to 2 grains per foot of PETN, RDX, HMX, lead styphnate or azide, nitromannite, picryl sulfone, or bis(trinitroethyl)urea within a metal sheath is capable of propagating the detonation, whereas such cores of tetryl or trinitrotoluene are unsatisfactory. Therefore, the critical feature of the present invention is the continuous column of a cap-sensitive crystalline high explosive selected from the former group in a quantity of from 0.1 to 2 grains per foot of length encased in a metal sheath. Below this weight-to-length range, the detonation generally will die out, and above this range, the resultant cords are of such brisance to be unsuitable for the desired applications.

The fact that explosive cores of such small quantities of explosive will propagate detonation is unexpected, and

i 6 an Wont Inn" nun/1 [In/112a natal startling is new In! far nun/2 pmpngnnbn. Although metal sheaf/IS of @55 lead and aluminum have been illustrated because of the availability and ease of application of these representative metals, other metals such as tin, silver, copper, mag- 5 1 ggf g zlltt tk nesium, etc. can be used. As previously stated, the a rn ttn' i h fla t 2 sheathed explosive core may be covered, or countered,

3 M No. 2 floltlblllil count with a variety of materials, such as woven fabric, ex- 4 Instmitc'orlleoutta i mini tmded synthetic polymeric compositions, and natural g gg 'g gggg-t gg t a double materials, for example, rubber. g ni 1? i i uliio i t a t it 2 Oi the highexplosive materials specified as being suit- 8 i Tg p gwi i tei i i .E?: f .??:i :%?f-

able, the exact material used will be determined by such factors as availability, economics, ease of handling, and Nos. 1-5 were determined experIirnentally fort llgtootr lengghs 0g tge the application in which the cord will be used. For indicated cord or fuse. alues fort 05.6-8 were a en rom oun D T. Jones, N.Y., Van Nostrand, 1937). appllcatlons m Winch a relatively high detonation velocity from the scope of the invention. We intend, therefore, be used. Naturally, the detonation velocity 18 also con 20 to be limited only by the f n i claim trolled somewhat by the amount of explosive within the We claim; given range which is usad- For example, PETN in the An explosive detonation conveying cord of low brisance amount of and grain P foot in 3 lfiad Sheath and producing little or no noise which comprises: a metal gives Velocities of about 5300 and 4200 meters P sheath encasing a continuous core of from 0.1 to 2 grains and, respectively. As exemplified, nitromannite in loadper foot of length of a granular cap-sensitive high exings of 1.9 and 1.0 grains per foot detonated at velocities plosive which retains its crystalline form at all temperaof 5600 and 3100 meters per second, respectively. turcs below 225 F. and selected from the group com The connecting cord of this invention is characterized isting of pcnta EIYEhIIIOitBUZlIIIU'RtQ cyclotrimethylene by uniform high velocity, low brisance, and the productrinitramine, cyclotetrarnethylenetetranitramine, nitrodmlantion of little noise. Therefore, the cord is particularly n1tt 1ead aZlde, lead YP P Y sllfonei i n 1; advantageous in such applications as those in which m r?ethyl)u(r1ea,han i1a covernlg ovetr :1 e rlnes'ia s ezattld to rein orce sai 5 cat agams ongi n ma ress shielding cannot be employed, for example the aforementioned bottom-hole priming, and those in which the Protect 1t agamst external Physical damage noise inherent in detonat ng fuse cannot be tolerated.

References Cited in the file of this patent Moreover, the low brisance of the cord which gives no 1 1 f h d t l 1 t UNITED STATES PATENTS atera transmission 0 t e etonation s imu us e imina es the possibility of the simultaneous detonation of all the k223i: 1 explosive within a coiled length, the detonation generally 40 1 3O6895 H arle June 1919 propagating through the core without damaging the 1741380 Smelling Dec 1926 countering material at all.

The following table is presented as indicative of the 1991857 Lewis 1935 noise level produced by the cord of the present invention FQREIGN PATENTS and conventional detonating fuse, in comparison with the 742,300 Great Britain Dec. 21, 1955 noise level produced by several common sources. 747,878 Great Britain Apr. 18, 1956 UNITED STATES PATENT ()FFICE @ERMMCATE U15 @QRREQTEGN Patent No 2 982 21O May 2 1961 David J., Andrew et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 2 line 10 for "year" read yard --B Signed and sealed this 31st day of October 1961a (SEAL) Attest:

ERNEST W. SWIDEB DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Eatent No. 2382,21!) May 2 1961 David J. Andrew et al.

ertified that error appears in the above numbered pat- It is hereby c that the said Letters Patent. should read as ent requiring correction and corrected below Column 2', line 10, for "year" read yard Signed and sealed this 31st day of October 1961.

' '(Cs EAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents USCOMM-DC- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2982,210 May 2 1961 David L Andrew et a1.

It is hereby certified that error appears fin the above numbered patent requiring correction and that the said Letters Patent. should read as corrected below Column 2,, line 10 for year read yard (s EAL) Attest:

ERNEST W. SWIDER Attesting Officer I DAVID L. LADD Commissioner of Patents USCOMM-DC 

